Project Summary Antimicrobial resistance (AMR) has spread rapidly around the globe in both developing and developed countries, making it an eminent threat to the society. Once powerful antibiotics have now become virtually useless. The situation is especially dire for Gram-negative bacteria where the vast majority of antibiotics are no longer effective, and there has been no new class of clinically-approved antibiotics for Gram-negative bacteria for almost 50 years. A key reason for this crisis is the inability of drug molecules to penetrate the cell envelop which has an additional outer membrane in Gram-negative bacteria. New strategies that can help antibiotics to traverse this barrier and accumulate inside the bacterium will revive and extend the lifespan of current antibiotics, having an immediate socioeconomic impact of saving lives and lowering the healthcare cost. We discovered that certain sugars, when conjugated onto nanoparticles, could significantly increase the surface binding and penetration of nanoparticles into the bacterium. These are bacterium-specific sugars as they are important for the survival of the bacterium but are not expressed by human cells. Our objective is to understand how exactly these unique sugars help nanoparticles penetrate the bacterial cell envelop, as well as to use these unique sugars to guide the targeted delivery of antibiotics into the bacterium. The approach is innovative because it uses bacterium-specific sugars to target bacteria but not the human cells. The project is significant because it represents a new way to overcome the penetration barrier, which will make bacteria vulnerable again to otherwise useless antibiotics. In Aim 1 of this project, we will conduct mechanistic investigations on how unique sugars mediate the uptake of nanomaterials by bacteria, and which cell wall components constrain the interaction and uptake. Understanding this process is invaluable, serving to fill important knowledge gaps, for example, how nanoparticles penetrate bacterial cell envelope in general. In Aim 2, we will use unique sugars to guide the targeted delivery of antibiotic- loaded liposomes to bacteria. We hypothesize that the bacterium-specific sugars will enhance the fusion/penetration of antibiotic-loaded liposomes with bacterial cell membrane, overcoming the penetration barrier and releasing antibiotics into the bacterium at high local doses. The outcome will re-establish the effectiveness of common antibiotics against otherwise untreatable resistant bacteria. This AREA grant will provide stimulating training for 2 PhD and ~3 undergraduate students, engaging them in biomedical research and preparing them for their future careers in biomedical sciences. The research is unique to the University. It will enhance biomedical research activities and contribute to improving the general research environment on campus.